An electrochemical gas sensor with a plurality of electrodes and a measuring electrode made of diamond-like carbon (DLC) is known from DE 199 39 011 C1. The measuring electrode is produced by means of a coating method, in which diamond-like carbon is applied to a gas-permeable membrane by means of a sputtering method. Measuring electrodes made of DLC have very high long-term stability. However, only a small number of gases can be directly reacted on them, and a mediator is therefore necessary, which oxidizes or reduces the analyte to be measured, while it undergoes reduction or oxidation itself and is again re-oxidized or re-reduced on the measuring electrode. The development of suitable mediators is very demanding, because these must react selectively with the analyte to be measured and must be re-oxidized or re-reduced on the DLC measuring electrode.
An electrochemical gas sensor with a measuring electrode made of boron- or nitrogen-doped diamond (BDD) is disclosed in DE 101 44 862 A1. The measuring electrode material is applied as a thin layer to a porous, gas-permeable substrate. Such measuring electrodes have very high long-term stability and have an extremely large potential window, so that even very difficult-to-oxidize substances (analytes and mediators) can be reacted. Besides the high price compared to other electrode materials, their use in electrochemical gas sensors causes considerable problems in terms of design.
An electrochemical measuring device, in which the measuring electrode has carbon nanotubes, is known from EP 1 544 607 A1. The carbon nanotubes are embedded in an insulator such that contact with the electrolyte is possible on the surface only. Such an electrode design is not suitable for a gas sensor because uniform wetting of the side of the electrode surface facing the gas is not guaranteed.